As shown in FIGS. 1 and 2, a conventional compressor of the type mentioned above has a hermetic container 101 in which is fixed a stator 104 of an electric motor 103 for driving a compression mechanism 102. A crankshaft 106 for driving the compression mechanism 102 is connected to a rotor 105 of the electric motor 103. The bottom of the hermetic container 101 forms a lubricant reservoir 107. The compression mechanism 102 includes: a stationary scroll member 110 having a stationary frame 108 and a stationary spiral wrap 109 formed integrally with the stationary frame 108; an orbiting scroll member 113 having an orbiting scroll wrap 111 which meshes with the stationary sprial wrap 109 to form a plurality of compression working chambers 114 therebetween, and an orbiting end plate 112 on which the orbiting scroll wrap 111 is formed; and a rotation prevention member 115 which prevents the orbiting scroll member 113 from rotating about its own axis so as to allow the orbiting scroll member 113 only to orbit. An orbiting drive shaft 116 which is disposed on the side of the orbiting end plate 112 opposite to the orbiting scroll wrap 111 is received in an eccentric bearing 118 provided inside of a main shaft 117 which is formed on one end of the crankshaft 106. The crankshaft 106 is supported by a main bearing assembly 120 having a main bearing 119 which supports the main shaft 117 and an upper bearing assembly 122 having a slide-type upper bearing 121 which supports the end of the crankshaft 106 opposite to the main shaft 117. A thrust bearing 123 fixed to the main bearing assembly 120 bears axial thrust on the orbiting end plate 112. In operation, a gaseous refrigerant sucked from a suction pipe 124 connected to the compressor is introduced into the compressor 102 through a suction port 125 of the compression mechanism 102 and is compressed in the compression working chamber 114. The compressed gaseous refrigerant is discharged through a discharge port 126 and is delivered to the exterior of the compressor through a discharge chamber 127 and a discharge pipe 128 (refer to Japanese Patent Laid-Open Publication No. 1-177482).
In this known compressor, the crankshaft 106 is supported at its both ends so as to hold the rotor 105. Therefore, no substantial moment is applied to the main bearing 119 and the moment which acts to bend the crankshaft 106 is small, thus contributing to improvement in the reliability of the compressor. This arrangement, however, poses a problem that the rotary shafts including the crankshaft 106 tends to be mounted in a wrong manner during the assembly of the compressor, resulting in troubles such as vibration or breakdown of the bearings. Furthermore, the upper bearing 121 tends to suffer from a shortage of lubricant so that this bearing, which is of slide bearing type, runs a risk of damage. An arrangement shown in FIG. 2 has been proposed to overcome the abovedescribed problem. In this arrangement, a crankshaft 201 is supported at its end opposite to a main shaft 202 by an upper bearing 203 of rolling type. In contrast to a slide-type bearing, a rolling type bearing can bear both radial and axial loads and requires a smaller amount of lubricant than the slide-type bearing. The use of the rolling type bearing, therefore, provides a greater tolerance for assembly precision and reduces the requirement for lubrication (refer to, for example, Japanese Patent Laid-Open Publication Nos. 1-170779, 58-172485 and 62-253982). The rolling type bearing, however, poses another problem: namely, increase in vibration and noise due to axial vibration and resonance.